Personally, I would only ever use a centre one-way when running a front way.
Basically, if you use dual one-ways, it helps cancel the drag from the front drivetrain, and also reduces any possibility of a tweak effect sue to spinning differences in the front one-way bearings. I also find that using dual one-ways really helps to smooth out the car going into a turn.
Some people have commented that you loose a little throttle response when running a centre one-way, but I can't say i ever noticed that.
As also mentioned, you will loose the braking ability, as it is like applying a handbrake on a real car, as the brakes will only act on the rear wheels. In escense, a one way is good for a track or class where you don't require brakes... stock carpet is a good one
As for cancelling each other out...